High Planting Rates Improve Weed Suppression, Yield, and Profitability in Organically-Managed, No-till–Planted Soybean

Abstract

High soybean populations have been shown to hasten canopy closure, which can improve both weed suppression and soybean yield. In conventional soybean production, the high cost of genetically engineered seed and seed treatments have led growers to plant at lower rates to maximize profitability. For organic farmers, market price premiums are typically double the price received for conventional soybean. Without chemical or mechanical weed management, cultural practices are particularly important for adequate weed suppression in cover crop–based organic no–till planted soybean production. In 2014, an experiment was conducted in Aurora and Hurley, New York, to assess the effects of increasing soybean planting rates on weed suppression, soybean yield, and partial economic return. Five planting rates ranging from 195,000 to 914,000 seedsha−1were arranged in a randomized complete block design. As soybean planting rate increased, weed biomass decreased and soybean yield increased at both sites. An asymptotic model described the relationship between increasing soybean planting rate and yield, and the estimated maximum yield was 2,504 kgha−1in Aurora and 3,178 kgha−1in Hurley. Despite high soybean populations, minimal lodging was observed. Partial returns decreased beyond the predicted economically optimal planting rate of 646,000 seeds ha−1in Aurora and 728,000 seeds ha−1in Hurley as higher seed costs were no longer offset by yield gains. Based on our results, planting rates that are more than double the recommended rate of 321,000 seeds ha−1for wide row (≥76 cm) conventional soybean management in New York can enhance weed suppression, increase yield, and improve profitability in organic no-till planted soybean production.